Merge pull request #2513 from plotly/fix/#2512

Raise error when iterating over patch objects.

Author: T4rk1n

Diff for: CHANGELOG.md

@@ -9,6 +9,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#2508](https://github.com/plotly/dash/pull/2508) Fix error message, when callback output has different length than spec
 - [#2207](https://github.com/plotly/dash/pull/2207) Fix object of components support.
 - [#2500](https://github.com/plotly/dash/pull/2500) Passing customdata by click for scattermapbox, fix [#2493](https://github.com/plotly/dash/issues/2493)
+- [#2513](https://github.com/plotly/dash/pull/2513) Raise error when iterating over patch objects, fix [#2512](https://github.com/plotly/dash/issues/2512)
 
 ## Updated
 

Diff for: dash/_patch.py

@@ -99,6 +99,12 @@ def __ior__(self, other):
         self.update(E=other)
         return _noop
 
+    def __iter__(self):
+        raise TypeError("Patch objects are write-only, you cannot iterate them.")
+
+    def __repr__(self):
+        return f"<write-only dash.Patch object at {self._location}>"
+
     def append(self, item):
         """Add the item to the end of a list"""
         self._operations.append(_operation("Append", self._location, value=item))

Diff for: tests/unit/test_patch.py

@@ -255,3 +255,11 @@ def test_pat020_patch_pickle():
     q = pickle.loads(data)
 
     assert patch_to_dict(p) == patch_to_dict(q)
+
+
+def test_pat021_patch_iter():
+    p = Patch()
+
+    with pytest.raises(TypeError):
+        for _ in p["invalid"]:
+            print("invalid iteration")